Copolymer-1 is a synthetic peptide analog of myelin basic protein (MBP), which is a natural component of myelin sheath. It is a non-autoantigen, which suppresses experimental allergic encephalomyelitis (EAE) induced by various encephalitogens including mouse spinal cord homogenate, which includes all myelin antigens such as myelin basic protein. Copolymer-1 has been demonstrated to be active when injected subcutaneously, intra-peritoneally, intravenously or intramuscularly. It is known that Copolymer-1 is used in the treatment of multiple sclerosis.
Reference may be made to U.S. Pat. No. 3,849,550 wherein they claim a process wherein the N-carboxyanhydrides (NCA) of tyrosine, alanine, γ-benzyl glutamate and Nε-trifluoro-acetyl lysine are polymerized at ambient temperature in anhydrous dioxane with diethylamine as initiator.
Reference may be made to U.S. Pat. No. 5,800,808 wherein they claim a method of manufacturing copolymer-1, comprising reacting protected copolymer-1 with hydrobromic acid to form trifluoroacetyl copolymer-1, treating said trifluoroacetyl copolymer-1 with aqueous piperidine solution to form copolymer-1, and purifying said copolymer-1, to result in copolymer-1 having a molecular weight of about 5 to 9 kilodaltons.
Reference may be made to U.S. Pat. No. 5,981,589 wherein they claim a process for the manufacture of copolymer-I, comprising reacting protected copolymer-I with hydrobromic acid to form trifluoroacetyl copolymer-I, treating the said trifluoroacetyl copolymer-I with aqueous piperidine solution to form copolymer-I and purifying said copolymer-1, to result in copolymer-1 having a molecular weight of about 5 to 9 kilodaltons. The method involves use of non-supported diethylamine as initiator.
Reference may be made to U.S. Pat. No. 3,849,550 wherein they claim a process for the preparation of a polypeptide-I composed of the following amino acid units in the structure namely: L-alanine, L-glutamic acid, L-lysine and L-tyrosine randomly arranged in the polypeptide comprising polymerization of a mixture of the N-carboxyanhydrides of L-alanine, L-tyrosine, a protected L-glutamate and a protected L-lysine to obtain protected copolymer-6 or salts thereof.
But the prior art documents do not present a process for the synthesis of co-polymer-I with control over specific molecular weight range. Further, in the prior art processes it is observed that when polymers are isolated from amine-initiated polymerization reaction mixtures and carefully freed from unreacted anhydrides, they have residual levels of acid groups titratable by sodium methoxide in various anhydrous solvents, as cited in sela et al in J. Am. Chem. Soc. Apr. 5, 1955, volume 77, page 1893-1898. Also, U.S. Pat. No. 6,620,847 has shown in example 2 that when the % of high molecular weight of co-polymer-1 species is less than 2.5%, the % release of serotonin, indicative of toxicity is low, and vice-versa. Further in the same example the inventors have specified that the copolymer with average molecular weight of 22 KDa was designated toxic.
Thus there exists a need in the art to have a process for the synthesis of co-polymer 1 wherein the molecular weight of co-polymer is controlled below 22 KDa, preferably below 20 KDa to overcome toxicity related issues. Also, the process should result in the co-polymer 1 product without the residual levels of acids. Further the process should be simple and efficient, using commonly available chemicals and result in the product directly, with a high degree of purity, not requiring any more steps to for separation, purification, fractionation of various molecular weight ranges and such like.
Novelty of the present invention lies in the process of preparation of Copolymer-I using polymer bound catalyst as initiator. The Copolymer-I obtained in the present invention has acid content of less than 1%.